In recent years, MEMS (Micro Electro Mechanical System) which has been attracting attention as a mass production system that realizes high performance and high degree of integration by integrating minute parts within a single chip utilizing a semiconductor manufacturing technology is expected for development in a variety of fields such as fields of information and telecommunications, as well as automobiles, consumer appliances, and medical and bio-related fields. Demands for downsizing in each of these fields have been increasingly growing, and exploitation of a photosensitive resin composition capable of forming a micro resist pattern having a large film thickness and a high aspect ratio has been desired.
However, conventional photosensitive resin compositions including a novolac resin and diazonaphthoquinone as a photoacid generator could not provide a profile having a high aspect ratio in the case with a large film thickness. This results from the diazonaphthoquinone type photoacid generator that exhibits high absorption of near ultra violet light used in exposure, leading to large difference in exposure intensity between the top and bottom of a thick film, whereby the resulting resin pattern has a tapered or curved profile as a consequence.
Taking into consideration such circumstances, a photosensitive resin composition containing an epoxy resin and an acid generator was proposed as a photosensitive resin composition capable of forming a micro resist pattern with a high aspect ratio. Specifically, a photosensitive resin composition including an epoxy-functional novolac resin, an acid generator such as a triarylsulfonium salt, and a diluent capable of reacting with an epoxy-reactive group is disclosed (for example, see Patent Document 1). Furthermore, a photosensitive resin composition including a polyfunctional bisphenol A formaldehyde-novolac resin, triphenylsulfonium hexafluoroantimonate as an acid generator, and a cyclopentanone solvent, and capable of forming a thick film is disclosed (for example, see Patent Document 2).
On the other hand, photosensitive resin compositions that provide high sensitivity and high resolving ability were proposed in addition to the diazonaphthoquinone type photoacid generator. For example, a photosensitive resin composition prepared using an aromatic sulfonium cation polymerization initiator is disclosed (see Patent Documents 3 and 4). Moreover, a permanent film resist composition containing a cation polymerization initiator that absorbs exposure light of a wavelength of 360 nm or longer is disclosed (see Patent Document 5).
The aforementioned photocation polymerization initiator is generally constituted with a cation component and an anion component. Examples of the anion component include SbF6−, AsF6−, PF6−, BF4− and the like, and known order of the sensitivity is represented by SbF6−>AsF6−>PF6−>BF4−. Thus, antimony (Sb) based, or arsenic (As) based cation polymerization initiators that are highly sensitive have been widely used.
However, since antimony is a deleterious substance, and arsenic is a toxic substance, to use these compounds is not preferred in light of safety aspects. Accordingly, as the cation polymerization initiator including neither antimony nor arsenic, onium fluorinated alkyl fluorophosphates are disclosed (see Patent Document 6).
Patent Document 1: Japanese Examined Patent Application Publication No. H07-78628
Patent Document 2: U.S. Pat. No. 6,391,523
Patent Document 3: Japanese Unexamined Patent Application Publication No. H09-268205
Patent Document 4: Japanese Unexamined Patent Application Publication No. 2005-055865
Patent Document 5: Japanese Unexamined Patent Application Publication No. H10-097068
Patent Document 6: International Publication No. 2005/116038